It will be described with reference FIGS. 6 to 8. FIG. 6 is a configuration view of a seat, FIG. 7 is an exploded perspective view showing a reclining device for a vehicle seat according to the prior art, and FIG. 8 is a configuration view explaining a locked state of the reclining device in FIG. 7.
As shown in FIG. 6, a seat 1 is configured by a seat cushion 2 that supports buttocks of a seated person, and a seat back 3 provided to be tiltable with respect to the seat cushion 2 in front and rear directions and to support a back of the seated person. A reference numeral 4 is a reclining device provided on a rotation axis for tilting of the seat back 3 to allow and restrict the tilting of the seat back 3.
Next, the reclining device 4 will be described with reference to FIGS. 7 and 8.
In these figures, the reclining device 4 includes a ratchet (first member) 7, in which internal teeth 7a are formed thereon along a circumferential direction of a circle about an axis of a relative rotation and one side is formed as an open side, and a base plate (second member) 5, which is stacked at the open side of the ratchet 7 and provided to be rotatable with respect to the ratchet 7 in the circumferential direction.
The base plate 5 is provided with two pawls 10 having an external tooth 10d to engage with the internal teeth 7a, respectively. The base plate 5 has a guide 5a and a guide 5b formed thereon to guide each pawl 10 in a radial direction with respect to the relative rotation. Therefore, each pawl 10 is movable in the radial direction with respect to the relative rotation.
On a surface opposite to a surface on which the external tooth 10d is formed of each pawl 10, a recess 10e is formed to extend in a direction intersecting with the radial direction with respect to the relative rotation.
A shaft 8 is rotatably provided along the axis of the relative rotation, and a rotating cam 9 including hook portions 9a having a hook shape is attached on the shaft 8 to be rotated together with the shaft 8. If the shaft 8 is rotated in one direction, each of the hook portions 9a of the rotating cam 9 presses the surface opposite to the surface on which the external tooth 10d is formed of each pawl 10, so that the pawl 10 is moved to a locked position where the external tooth 10d is engaged with the internal teeth 7a of the ratchet 7 (see FIG. 8). On the other hand, if the shaft 8 is rotated in the other direction, each of the hook portions 9a enters into the recess 10e of each pawl 10 and presses against an inner wall surface at a side of the rotation center of the relative rotation of the recess 10e, so that the pawl 10 is moved to an unlocked position where the external tooth 10d is disengaged from the internal teeth 7 of the first member 7.
Also, each pawl 10 is urged to be positioned at the locked position by a spiral spring 19, which has one end locked on the base plate 5 and the other end locked in a locking portion 9b of the rotating cam 9.
Operations of the reclining device will be described. Meanwhile, it is assumed that the ratchet 7 is provided on a seat back side and the base plate 5 is provided on a seat cushion side.
Generally, due to an urging force of the spiral spring 19, each pawl 10 provided on the base plate 5 is positioned at the locked position where the external tooth 10d is engaged with the internal teeth 7a of the ratchet 7, and as a result, the relative rotation between the ratchet 7 and the base plate 5 is restricted, and thus the seat back 3 becomes a state (locked state), where the seat back 3 cannot be rotated with respect to the seat cushion 2.
When the operation shaft 8 is operated against the urging force of the spiral spring 19 and thus the rotating cam 9 is rotated in the other direction, each pawl 10 is moved to the unlocked position where the external tooth 10d is disengaged from the internal teeth 7a, and as a result, the relative rotation between the ratchet 7 and the base plate 5 is enabled, and thus, the seat back 3 can be rotated with respect to the seat cushion 2.
If the operation force on the rotating cam 9 is released, the external tooth 10d of each pawl 10 provided on the base plate 5 is engaged with the internal teeth 7a of the ratchet 7 due to the urging force of the spiral spring 19, and thus the relative rotation between the ratchet 7 and the base plate 5 is restricted, so that it is to be the locked state again.